Split sole dance trainers are generally not worn by beginners (except those who want to look cool & don't like the style of full sole shoes) as they don't have arch support so you need to build up strength.

I'm not sure. From previous experience I know I wouldn't want to be twisting the feet and legs so much in normal trainers, but I guess it also varies class by class as they all differ in their impact and how dancey they are.

I'll only wear trainers for this anyway, so it's not as if it will be an additional outlay as I don't own any trainers as it is

I do zumba type classes in a regular cross trainer. I know people who are instructors and they look for cushioning in the front half of the foot and general cushioning, rather than a running style which is designed for impact in the heel. But that's about it.

It depends on the floor, they have just put rubber floors in to my gym which provides too much grip with normal trainers. It can damage your ankles and knees if you twist in your trainers but your shoes stick to the ground and the rest of your body moves

I do Zumba in my dance boots and it's great, they don't have very much grip and given that you should be doing about 90% of moves with the weight on your toes anyway, the arch support thing shouldn't be an issue